Abstract

A hallmark of aged mesenchymal stem/progenitor cells (MSCs) in bone marrow is the pivot of differentiation potency from osteoblast to adipocyte coupled with a decrease in self-renewal capacity. However, how these cellular events are orchestrated in the aging progress is not fully understood. In this study, we have used molecular and genetic approaches to investigate the role of forkhead box P1 (FOXP1) in transcriptional control of MSC senescence. In bone marrow MSCs, FOXP1 expression levels declined with age in an inverse manner with those of the senescence marker p16INK4A. Conditional depletion of Foxp1 in bone marrow MSCs led to premature aging characteristics, including increased bone marrow adiposity, decreased bone mass, and impaired MSC self-renewal capacity in mice. At the molecular level, FOXP1 regulated cell-fate choice of MSCs through interactions with the CEBPβ/δ complex and recombination signal binding protein for immunoglobulin κ J region (RBPjκ), key modulators of adipogenesis and osteogenesis, respectively. Loss of p16INK4A in Foxp1-deficient MSCs partially rescued the defects in replication capacity and bone mass accrual. Promoter occupancy analyses revealed that FOXP1 directly represses transcription of p16INK4A. These results indicate that FOXP1 attenuates MSC senescence by orchestrating their cell-fate switch while maintaining their replicative capacity in a dose- and age-dependent manner.

Abstract

Germline coding mutations in different telomere-related genes have been linked to autosomal-dominant familial pulmonary fibrosis. Individuals with these inherited mutations demonstrate incomplete penetrance of clinical phenotypes affecting the lung, blood, liver, skin, and other organs. Here, we describe the somatic acquisition of promoter mutations in telomerase reverse transcriptase (TERT) in blood leukocytes of approximately 5% of individuals with inherited loss-of-function coding mutations in TERT or poly(A)-specific ribonuclease (PARN), another gene linked to telomerase function. While these promoter mutations were initially identified as oncogenic drivers of cancer, individuals expressing the mutations have no history of cancer. Neither promoter mutation was found in population-based cohorts of similar or advanced age. The TERT promoter mutations were found more frequently in cis with the WT allele than was the TERT coding sequence mutation. EBV-transformed lymphoblastoid B cell lines (LCLs) derived from subjects with TERT promoter mutations showed increased telomerase expression and activity compared with cell lines from family members with identical coding mutations. TERT promoter mutations resulted in an increased proliferation of LCLs and demonstrated positive selection over time. The persistence and recurrence of noncoding gain-of-function mutations in these cases suggests that telomerase activation is not only safely tolerated but also advantageous for clonal expansion.

Abstract

Olfactory dysfunction is broadly associated with neurodevelopmental and neurodegenerative diseases and predicts increased mortality rates in healthy individuals. Conventional measurements of olfactory health assess odor processing pathways within the brain and provide a limited understanding of primary odor detection. Quantification of the olfactory sensory neurons (OSNs), which detect odors within the nasal cavity, would provide insight into the etiology of olfactory dysfunction associated with disease and mortality. Notably, OSNs are continually replenished by adult neurogenesis in mammals, including humans, so OSN measurements are primed to provide specialized insights into neurological disease. Here, we have evaluated a PET radiotracer, [11C]GV1-57, that specifically binds mature OSNs and quantifies the mature OSN population in vivo. [11C]GV1-57 monitored native OSN population dynamics in rodents, detecting OSN generation during postnatal development and aging-associated neurodegeneration. [11C]GV1-57 additionally measured rates of neuron regeneration after acute injury and early-stage OSN deficits in a rodent tauopathy model of neurodegenerative disease. Preliminary assessment in nonhuman primates suggested maintained uptake and saturable binding of [18F]GV1-57 in primate nasal epithelium, supporting its translational potential. Future applications for GV1-57 include monitoring additional diseases or conditions associated with olfactory dysregulation, including cognitive decline, as well as monitoring effects of neuroregenerative or neuroprotective therapeutics.

Abstract

Hutchinson-Gilford progeria syndrome (HGPS) is a rare autosomal dominant genetic disease that is caused by a silent mutation of the LMNA gene encoding lamins A and C (lamin A/C). The G608G mutation generates a more accessible splicing donor site than does WT and produces an alternatively spliced product of LMNA called progerin, which is also expressed in normal aged cells. In this study, we determined that progerin binds directly to lamin A/C and induces profound nuclear aberrations. Given this observation, we performed a random screening of a chemical library and identified 3 compounds (JH1, JH4, and JH13) that efficiently block progerin–lamin A/C binding. These 3 chemicals, particularly JH4, alleviated nuclear deformation and reversed senescence markers characteristic of HGPS cells, including growth arrest and senescence-associated β-gal (SA–β-gal) activity. We then used microarray-based analysis to demonstrate that JH4 is able to rescue defects of cell-cycle progression in both HGPS and aged cells. Furthermore, administration of JH4 to LmnaG609G/G609G-mutant mice, which phenocopy human HGPS, resulted in a marked improvement of several progeria phenotypes and an extended lifespan. Together, these findings indicate that specific inhibitors with the ability to block pathological progerin–lamin A/C binding may represent a promising strategy for improving lifespan and health in both HGPS and normal aging.

Abstract

The incidence of cancer is higher in the elderly; however, many of the underlying mechanisms for this association remain unexplored. Here, we have shown that B cell progenitors in old mice exhibit marked signaling, gene expression, and metabolic defects. Moreover, B cell progenitors that developed from hematopoietic stem cells (HSCs) transferred from young mice into aged animals exhibited similar fitness defects. We further demonstrated that ectopic expression of the oncogenes BCR-ABL, NRASV12, or Myc restored B cell progenitor fitness, leading to selection for oncogenically initiated cells and leukemogenesis specifically in the context of an aged hematopoietic system. Aging was associated with increased inflammation in the BM microenvironment, and induction of inflammation in young mice phenocopied aging-associated B lymphopoiesis. Conversely, a reduction of inflammation in aged mice via transgenic expression of α-1-antitrypsin or IL-37 preserved the function of B cell progenitors and prevented NRASV12-mediated oncogenesis. We conclude that chronic inflammatory microenvironments in old age lead to reductions in the fitness of B cell progenitor populations. This reduced progenitor pool fitness engenders selection for cells harboring oncogenic mutations, in part due to their ability to correct aging-associated functional defects. Thus, modulation of inflammation — a common feature of aging — has the potential to limit aging-associated oncogenesis.

Abstract

Dyskeratosis congenita (DC) and related syndromes are inherited, life-threatening bone marrow (BM) failure disorders, and approximately 40% of cases are currently uncharacterized at the genetic level. Here, using whole exome sequencing (WES), we have identified biallelic mutations in the gene encoding poly(A)-specific ribonuclease (PARN) in 3 families with individuals exhibiting severe DC. PARN is an extensively characterized exonuclease with deadenylation activity that controls mRNA stability in part and therefore regulates expression of a large number of genes. The DC-associated mutations identified affect key domains within the protein, and evaluation of patient cells revealed reduced deadenylation activity. This deadenylation deficiency caused an early DNA damage response in terms of nuclear p53 regulation, cell-cycle arrest, and reduced cell viability upon UV treatment. Individuals with biallelic PARN mutations and PARN-depleted cells exhibited reduced RNA levels for several key genes that are associated with telomere biology, specifically TERC, DKC1, RTEL1, and TERF1. Moreover, PARN-deficient cells also possessed critically short telomeres. Collectively, these results identify a role for PARN in telomere maintenance and demonstrate that it is a disease-causing gene in a subset of patients with severe DC.

Abstract

There is large variation in lifespan among different species, and there is evidence that modulation of proteasome function may contribute to longevity determination. Comparative biology provides a powerful tool for identifying genes and pathways that control the rate of aging. Here, we evaluated skin-derived fibroblasts and demonstrate that among primate species, longevity correlated with an elevation in proteasomal activity as well as immunoproteasome expression at both the mRNA and protein levels. Immunoproteasome enhancement occurred with a concurrent increase in other elements involved in MHC class I antigen presentation, including β-2 microglobulin, (TAP1), and TAP2. Fibroblasts from long-lived primates also appeared more responsive to IFN-γ than cells from short-lived primate species, and this increase in IFN-γ responsiveness correlated with elevated expression of the IFN-γ receptor protein IFNGR2. Elevation of immunoproteasome and proteasome activity was also observed in the livers of long-lived Snell dwarf mice and in mice exposed to drugs that have been shown to extend lifespan, including rapamycin, 17-α-estradiol, and nordihydroguaiaretic acid. This work suggests that augmented immunoproteasome function may contribute to lifespan differences in mice and among primate species.

Abstract

The number of newly formed neurons declines rapidly during aging, and this decrease in neurogenesis is associated with decreased function of neural stem/progenitor cells (NPCs). Here, we determined that a WIP1-dependent pathway regulates NPC differentiation and contributes to the age-associated decline of neurogenesis. Specifically, we found that WIP1 is expressed in NPCs of the mouse subventricular zone (SVZ) and aged animals with genetically enhanced WIP1 expression exhibited higher NPC numbers and neuronal differentiation compared with aged WT animals. Additionally, augmenting WIP1 expression in aged animals markedly improved neuron formation and rescued a functional defect in fine odor discrimination in aged mice. We identified the WNT signaling pathway inhibitor DKK3 as a key downstream target of WIP1 and found that expression of DKK3 in the SVZ is restricted to NPCs. Using murine reporter strains, we determined that DKK3 inhibits neuroblast formation by suppressing WNT signaling and Dkk3 deletion or pharmacological activation of the WNT pathway improved neuron formation and olfactory function in aged mice. We propose that WIP1 controls DKK3-dependent inhibition of neuronal differentiation during aging and suggest that regulating WIP1 levels could prevent certain aspects of functional decline of the aging brain.

Abstract

While murine-based systems to identify cancer-promoting agents (carcinogens) are established, models to identify compounds that promote aging (gerontogens) have not been described. For this purpose, we exploited the transcription of p16INK4a, which rises dynamically with aging and correlates with age-associated disease. Activation of p16INK4a was visualized in vivo using a murine strain that harbors a knockin of the luciferase gene into the Cdkn2a locus (p16LUC mice). We exposed p16LUC mice to candidate gerontogens, including arsenic, high-fat diet, UV light, and cigarette smoke and serially imaged animals to monitor senescence induction. We show that exposure to a high-fat diet did not accelerate p16INK4a expression, whereas arsenic modestly augmented, and cigarette smoke and UV light potently augmented, activation of p16INK4a-mediated senescence. This work provides a toxicological platform to study mammalian aging and suggests agents that directly damage DNA promote molecular aging.